The halogenated derivatives of (2,2)-paracyclophane having general formula: ##STR1## in which X is a halogen and in particular chlorine, and n is an integer from 1 to 4, and in particular dichloro-(2,2)-paracyclophane and tetrachloro-(2,2)-paracyclophane, are well known in literature and are generally utilized as intermediates in the preparation of the corresponding chlorinated poly-p.xylylene.
Said halogenated derivatives of (2,2)-paracyclophane, and in particular the chlorinated derivatives of said compound, are usefully employed in the preparation of films in the field of the conforming coating by application according to the technique based on vacuum vapor deposition and polymerization in situ.
For this kind of application, as is well known, the halogenated starting products must have certain characteristics, namely:
(a) they must be pure, i.e., they must consist of compounds having the desired degree of substitution, in order to obtain a satisfactory homogeneity of the films, and
(b) the isomeric composition of the fractions, at the same degree of substitution, must be constant, in order to have the same conditions of application and the same chemical-physical characteristics of the films obtained.
The method generally followed for the preparation of the halogenated derivatives of (2,2)-paracyclophane is that of subjecting to halogenation the previously formed (2,2)-paracyclophane, which is obtained by carrying out the Hofmann elimination from p.methylbenzyltrimethylammonium hydroxide, of formula: ##STR2## by this halogenation process carried out on previously formed (2,2)-paracyclophane it is not possible to prevent the generation of appreciable amounts of undesirable products. In particular, in the case of a dichlorination process, there are obtained not only the desired dichlorinated isomers of (2,2)-paracyclophane containing one chlorine atom on each ring, but also the undesired isomers having two chlorine atoms on one ring only and those with only one chlorine atom and/or with three chlorine atoms. These by-products lead, during the polymerization step, to the formation of copolymers of p-xylylene, chloro-p-xylylene and dichloro-p-xylylene having a hign nonhomogeneity in the distribution of chlorine on the rings of the polymeric chains. Furthermore, from these isomer mixtures it is impossible, by means of the conventional separation techniques, to obtain only the di-halogenated isomers having an equal number of halogen atoms on each ring.